1. Field of the Invention
The present invention relates to a molding machine and method for shaping a plastic or metal substance without producing undesirable burrs.
2. Description of the Related Art
Japanese laid-open patent publication No. 160518/90 discloses a molding machine for encapsulating a circuit or other electronic parts in resin (see FIG. 4). A lead frame is sandwiched between upper and lower molds. The lower mold has a cavity to receive an encapsulating material such as epoxy resin under pressure. A groove is defined around and spaced from the cavity to form a partition therebetween. A resilient gasket made of silicon rubber is fitted in the groove and projects slightly upwardly from the upper surface of the lower mold. When the upper and lower molds are clamped together, the gasket is elastically deformed to closely contact with the lead frame. However, the encapsulating resin still tends to leak between the lower surface of the lead frame and the partition, thereby producing undesirable burrs in the lead frame and the partition. This is due to the fact that the lead frame is placed in metal-to-metal contact with the end surface of the partition and a clearance of the order of a few microns remains between the lead frame and the partition. The resulting burrs in the partition not only physically damage tile gasket, but also cause the molten resin to leak from the mold cavity to thereby chemically damage the gasket. This results in a decrease in the service life of the gasket. Another problem with the resilient gasket is that it can not be so deformed as to closely contact with electronic parts which have irregular surfaces or complicated shapes.